Tropical Depression 3 forms near South Carolina

Tropical Depression Three has formed off the Southeast U.S. coast. Charleston, SC long range radar shows the slow development of a solid spiral band of thunderstorms to the southeast of the center, away from land. The storm is over waters of marginal warmth, about 27°C, a degree above the threshold of 26°C needed to sustain a tropical storm. The warm waters are very shallow, and the Tropical Cyclone Heat Potential is near zero, meaning we're unlikely to see rapid intensification of TD 3. Wind shear is about 15 knots over the storm, and is forecast to remain 10-15 knots over the next two days. There is some dry air over the Southeast U.S. that may get entrained into TD 3's circulation. TD 3 could intensify into a weak tropical storm, if the center manages to remain over water. None of the models forecast that TD 3 will intensify beyond a 50 mph tropical storm, and this is a reasonable forecast, due to the relatively cool water temperatures, moderate wind shear, and the presence of dry air nearby. Coastal areas of North Carolina are likely to get heavy rains from TD 3, but it remains to be seen if these rains will penetrate far enough inland to significantly alleviate drought conditions over the state. Heavy rains may also develop over South Carolina, but the main rain will probably remain offshore as the storm passes that state. TD 3 is unlikely to bring heavy rain to any other states, with the possible exception of Cape Cod and Nantucket, Massachusetts Monday/Tuesday.

Links to follow:
Charleston, SC long range radar
Southeast U.S. Marine observations and forecasts


Figure 1. Latest satellite image of TD 3.

Caribbean disturbance 94L
A well-organized disturbance in the Central Caribbean (94L) is bringing heavy rain and gusty winds to Haiti and Jamaica tonight. This afternoon's Hurricane Hunter flight was unable to find a closed surface circulation, and this evening's 6:51 pm EDT QuikSCAT pass also shows no surface circulation. An upper-level cold low centered over Cuba is bringing about 20 knots of wind shear to the northern portion of 94L, but the southern portion of the disturbance is under only about 10 knots of wind shear.

The upper-level low is forecast to slide westward and weaken over the next two days, bringing low wind shear of 5-10 knots over the disturbance Saturday and Sunday. The low shear combined with the warm (28.5°C) water of the Western Caribbean should allow 94L to finally organize into a tropical depression as early as Saturday afternoon. NHC is giving 94L a high (>50% chance) of developing into a tropical depression by Sunday morning. Another Hurricane Hunter mission is scheduled to fly into 94L at 2 pm EDT Saturday. The disturbance has time to potentially strengthen into a tropical storm with 50 mph winds before coming ashore on the Yucatan Peninsula sometime between Sunday night and Monday afternoon. Passage over the Yucatan will no doubt significantly disrupt what should be a relatively weak system, and it is unclear what threat, if any, the storm will pose to the Gulf of Mexico coast. Once it does cross into the Gulf, wind shear should be low enough to permit development.

Bertha
Hurricane Bertha is still out there. I find it amazing we've had a July storm that has lasted 17 days and counting! Bertha's days are numbered, though. Bertha will reach cold water less than 70°F by Sunday, which should finally kill it.

I'll have a full update on the tropics Saturday morning. Boy, it sure looks like more like September than July in the tropics!

Jeff Masters